Field of the Invention
The invention relates to a method for producing at least one semiconductor body. The semiconductor body is formed of a layer sequence with at least one active zone that is applied to a semiconductor wafer by metal organic vapor phase epitaxy, and in which the layer sequence is provided with at least one mesa trench. It relates in particular to a method for producing light emitting diode (LED) chips with a mesa structure by metal organic vapor phase epitaxy (MOVPE).
A method for producing MOVPE LED chips is known for instance from U.S. Pat. No. 5,233,204. In it, by metal organic vapor phase epitaxy (MOVPE), a heterostructure including an n-conductive first InGaAlP boundary layer, an n-conductive active InGaAlP layer, and a p-conductive second InGaAlP boundary layer are deposited on a GaAs semiconductor wafer. A window layer of AlGaAs, GaAsP or GaP is applied by epitaxy to the second InGaAlP boundary layer. Next, an underside contact metallizing is applied to the underside of the semiconductor wafer, and a plurality of top contact metallizings are applied to the top side of the window layer. The semiconductor wafer is subsequently divided up into individual LED chips by sawing or diamond-wheel dicing.
In the LED chips, the window layer serves first to attain a lateral current propagation as much as possible over the entire cross section of the p-n junction, and second to increase the surface area of the LED chips that is available for light output. The ratio between the area of the semiconductor body covered by the top contact to the free surface area of the semiconductor body is increased. However, a large proportion of the radiation generated in the active zone is still lost by the total reflection at the surface of the LED chip.
Furthermore, when the semiconductor wafer is sawed or diced, destruction to the side faces of the epitaxial layers occurs, which among other things causes faster aging (degradation in the brightness of the LED over time) of the LED chips.
From Published, Non-Prosecuted German Patent Application DE 43 05 296 A1, corresponding to U.S. Pat. No. 5,429,954, a method for producing an LED is known in which mesa trenches are formed by wet-chemical etching in a layer sequence applied epitaxially to a substrate body, in order to improve the radiation power.
Such a wet-chemical etching process, however, in LED chips made by MOVPE, leads to selective etching of the MOVPE layer sequence. This creates so-called "mushroom" structures, which in semiconductor chips are provided with plastic sheathing because of mechanical stress, again causing faster aging (degradation in the electrical properties over time).
In U.S. Pat. No. 5,309,001, an MOVPE LED chip with a mesa structure is described that is made by wet-chemical etching or by reactive ion beam etching. The external quantum efficiency of such diodes, however, is still very low.